(In one case, ION LT, I rigged things differently because the ION spring behavior changes when in touring mode.) To finish, I slung a load cell (force gauge) on Spectra cord, and drilled a pair of holes in a steel bar that sits over the heel pins, attached to the load cell and windlass. Using my trusty desktop box of silicon and copper, I found a basic formula for spring rate, really basic, just force divided by distance, providing a number that allows comparison between different springs.Ī digital caliper provided the throw/distance instrument. So I researched the basic calculation for “spring rate,” which is how the “stiffness” of a spring is expressed as a number. That seemed crude - the kind of thing that would get me some something along the lines of a hockey puck to the face from certain Canadian individuals. Other, more complex bindings, including alpine bindings, place the heel unit on a track, with a spring that allows movement while keeping the heel unit in position.Īt first, I planned a simple yank on the bindings and through a process of gut feeling, or perhaps a load cell, gain a sense of the force required to compress the flex compensation spring. The simplest tech bindings accomplish this with an air gap ( tech gap) behind the boot heel. For those of you who’ve lived in a snowcave for the past twelve years, know that any ski binding has to somehow allow for ski flex shortening the distance between the heel and toe units of the binding. Underside of G3 ZED, showing flex compensation spring. But one wonders (as I ruminate on below as well), why not just provide an old style tech gap and be done with it? The answer to that question involves everything from product liability to ISO/DIN politics. Granted, a smooth, reliable spring such as that of the ZED, many other touring bindings, and all alpine bindings, is the standard of ski binding engineering. We’ve come to call this the “tech gap.” Some tech gaps were about 6 millimeters, and binding/boot combo could easily be built to that, or in my opinion a few millimeters more. Why? The original tech binding design provided ski flex compensation by providing a gap between the boot heel and binding, along with allowing the boot heel fittings to slide fore/aft on the binding heel pins. Any aficionado of tech bindings will find it ironic that the ZED travel, created by a complex spring and housing configuration, is now 6.8 millimeters. Important note regarding the ZED changes. If I stomped my heel down somewhat gently, still no obvious movement. Movement was imperceptible when I made a normal, simulated stride. The 20/21 version moves as well, but MUCH LESS EASILY (and with less maximum possible distance). The 19/20 version moved in my opinion all too easily, even with my below average body weight and no backpack. In our original blog post below, we determined that the geometry of the heel lifter is likely the primary cause of the heel unit movement. That’s a ~72% increase! Will this fix the problem some skiers have with this shifting/movement? Read on. So, how did the spring rate measure out in comparison to the 2019/20 version of the ZED heel? Check our spreadsheet windowed below. In theory, both these changes will reduce the likelihood of annoying heel unit movement while in touring mode (see video near bottom of post.) Moreover, I suspect the new spring might be a bit stiffer, but additional pre-loading, compared to previous configuration, might be the more important operative mechanism here. Along with that, G3 reduced the flex compensation travel distance ~2.8 mm, from ~9.6 mm to ~6.8 mm. This preloads the spring, and makes an easily tested/verified difference in spring rate. They thickened the housing on one end of the spring, by 1.5 millimeters. The unit is nearly identical, with one possibly key change. After we published the post below, G3 was kind enough to send us an updated ZED heel unit, due for distribution fall of 2020. 2020/2021 ZED heel to left, viewed from beneath showing ski flex compensation spring.
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